Method for selecting multiple customer premises equipments to share a channel in a wireless communications network

ABSTRACT

A method is proposed for selecting multiple customer premises equipments (CPEs) to share a channel in a wireless communications network. The method includes calculating a correlation between spatial signatures of every two CPEs subscribing to a base transceiver station (BTS) of the wireless communications network, wherein two CPEs constitute channel-sharing candidates if their correlation is lower than a predetermined threshold, creating a first set of CPEs of all the member of channel-sharing candidates, counting a number of channel-sharing candidates a CPE relates to for every CPE, selecting a first CPE related to the fewest number of channel-sharing candidates, creating a second set of CPEs by identifying all the CPEs that the first CPE relates to, and selecting a second CPE related to the fewest number of channel-sharing candidates from the second set of CPEs, wherein the first and second CPEs become two selected CPEs to share the channel.

CROSS REFERENCE

The present application claims the benefit of U.S. Provisional Application Ser. 60/836,719, which was filed on Aug. 10, 2006.

BACKGROUND

Spatial division multiple access (SDMA) increases the capacity of a wireless communications network by allowing more than one wireless station to access a communication channel on the same frequency at the same time. One example of channel sharing is that wireless stations, such as customer premises equipments (CPEs), transmit signals on the same frequency at different times or on different frequencies at the same time.

How to select a set of CPEs to share a communication channel is a very complicated and computationally intensive process. This is true primarily because not every CPE can share a communication channel with other CPEs in a wireless communications network employing SDMA.

There are a number of reasons why some CPEs cannot share a communication channel. One of the reasons is co-channel interference (CCI), which occurs when a CPE receives unintended signals from other CPEs sharing the same communication channel. This type of inter-user interference is the major drawback of an SDMA system. To suppress inter-user interference, an SDMA system must provide a means to isolate the spatial signatures of one CPE from those of the rest of the CPEs sharing a channel. Otherwise, inter-user interference may cause a communication channel to be unusable for the entire set of CPEs.

A second reason is that different CPEs may subscribe to the services of a base transceiver station (BTS) at any given time. In other words, a set of CPEs sharing a communication channel at one point in time may not be the same set of CPEs sharing the same communication channel at another time. A third reason is that the characteristics of the radio link may change over time.

In a conventional method, a BTS selects an optimal set of CPEs to permanently share a communication channel in a wireless communications network employing SDMA, based on certain predetermined parameters. The optimal set of CPEs chosen to share a communication channel at one time might not be optimal at a later time. Therefore, the permanent grouping of CPEs to share a communication channel is ineffective and inefficient.

What is desired is a system and method for improving the grouping of CPEs dynamically in a wireless communications network employing SDMA that addresses the dynamic nature of the radio link and participants of communication sessions.

SUMMARY

The present invention discloses a method for selecting multiple customer premises equipments (CPEs) to share a channel in a wireless communications network. The method is comprised of calculating a correlation between spatial signatures of every two CPEs subscribing to a base transceiver station (BTS) of the wireless communications network, wherein two CPEs constitute channel-sharing candidates if their correlation is lower than a predetermined threshold, creating a first set of CPEs of all the members of channel-sharing candidates, counting a number of channel-sharing candidates a CPE relates to for every CPE, selecting a first CPE related to the fewest number of channel-sharing candidates, creating a second set of CPEs by identifying all the CPEs that the first CPE relates to, and selecting a second CPE related to the fewest number of channel-sharing candidates from the second set of CPEs, wherein the first and second CPEs become two selected CPEs to share the channel.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. The invention may be better understood by reference to one or more of these drawings in combination with the description presented herein. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale.

FIG. 1 is a flow diagram illustrating a method to have a channel shared by two customer premises equipments based on the isolation of spatial signatures.

FIG. 2 is a flow diagram illustrating a second method to have a channel shared by two CPEs based on both the isolation of spatial signatures and path loss.

DESCRIPTION

The following detailed description of the invention refers to the accompanying drawings. The description includes exemplary embodiments, not excluding other embodiments, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

The method and system disclosed in the present invention reduces inter-user interference and improves the bit error rate (BER) for a group of CPEs in a wireless communications network employing SDMA. The selection of a group of CPEs to share a communication channel is based on the isolation of spatial signatures and path loss differences. The method and system disclosed in the present invention is applicable to any wireless communications network and the term channel refers to any of the conventional multiple access channels such as frequency, time, code or any combination of them. The method can be extended to include more than two CPEs, but the present invention discloses how to select two CPEs to share a communication channel.

Assume that there are K CPEs that subscribe to the services of a BTS in a cell of a wireless communications network employing SDMA. By using the method disclosed in the present invention, the BTS dynamically decides which CPEs would share a communication channel.

FIG. 1 is a flow diagram illustrating a method to have a channel shared by two CPEs based on the isolation of spatial signatures.

Let {C₁, C₂, . . . , C_(K)} denote the set of K CPEs subscribing to the services of the BTS equipped with M antennas. Let the spatial signature of CPE C_(i) be denoted as

${h_{i} = \begin{bmatrix} h_{i,1} \\ h_{i,2} \\ \vdots \\ h_{i,M} \end{bmatrix}},$

where m ∈(1,2, . . . ,M) and h_(i,m) is a spatial signature associated with antenna m.

Each CPE C_(i) is a candidate for sharing a communication channel with another CPE C_(j). A partner set χC _(i) which includes all the CPEs that could share a communication channel with the CPE C_(i), is created for each CPE C_(i). The number of CPEs in the set χ_(C) _(i) is denoted as n_(C) _(i) . A number set, denoted as χ_(pre) _(—) _(number)={n_(C) ₁ , n_(C) ₂, . . . , n_(C) _(k) }), is formed to show the number of partners of each CPE C_(i).

In step 110, for each C_(j) where 1≦j≦K and i≠j, the correlation s_(i) ^(j) between CPE C_(i) and CPE C_(j) is calculated according to the following equation:

$s_{i}^{j} = {{{h_{i}^{H}h_{j}}} = {{{\sum\limits_{m = 1}^{M}{h_{i,m}^{*}h_{j,m}}}}.\mspace{14mu} (\ldots)^{H}}}$

denotes a Hermitian operator. If s_(i) ^(j)

γ₀, where γ₀ is a predetermined threshold and 0≦γ₀≦1, then C_(j) is included in the partner set χ_(C) _(i) of CPE C_(i).

The number of CPEs in the partner set of CPE C_(i) is denoted as n_(C) _(i) . If n_(C) _(i) >0, C_(i) is included in a set χ_(pre), i.e., χ_(pre)∪χ_(pre){C_(i)} and n_(C) _(i) is included in the χ_(pre) _(—) _(number). The set χ_(pre) contains the CPEs that are pre-qualified to share a communication channel with another CPE. Step 110 is repeated for every CPE in the set {C₁, C₂, . . . , C_(K)}.

In Step 120, the smallest element of χ_(pre) _(—) _(number) is selected. If more than one n_(C) _(i) has the same smallest value, a predetermined tie-breaker rule is employed to select only one n_(C) _(i) For example, the first one of at least two CPEs that have the same smallest number in the χ_(pre) _(—) _(number) is selected. In other words, CPE C_(i) with the smallest number of partners is chosen to be one of the two CPEs selected to share a communication channel.

In step 130, let χ_(peer)=χ_(C) _(j) . For each CPE C_(j) in the χ_(peer), the partner set of C_(i), n_(C) _(j) is included in the set χ_(peer) _(—) _(number).

In step 140, the smallest element of χ_(peer) _(—) _(number) is selected. If more than one n_(C) _(j) has the same smallest value, a predetermined tie-breaker rule is employed to select only one n_(C) _(j) . In other words, CPE C_(j) with the smallest number of partners, is chosen to be the other CPE that is to share a communication channel. A pair of CPEs (C_(i), C_(j)) is identified to share a communication channel.

In Step 150, CPEs C_(i) and C_(j) are removed from the χ_(pre); n_(C) _(i) and n_(C) _(j) are removed from the χ_(peer) _(—) _(number) If there is more than one element in χ_(pre), the pairing process repeats from step 120. The process continues until no more CPEs could share a communication channel. All feasible CPE pairs in SDMA are identified.

FIG. 2 illustrates a second method to have a channel shared by two CPEs based on the isolation of spatial signatures and path loss.

Let {C₁, C₂ , . . . , C_(K)} denote the set of K CPEs subscribing to the services of the BTS equipped with M antennas. Let the spatial signature of CPE C_(i) be denoted as

${h_{i} = \begin{bmatrix} h_{i,1} \\ h_{i,2} \\ \vdots \\ h_{i,M} \end{bmatrix}},$

where m ∈(1,2, . . . ,M) and h_(i,m) is a spatial signature associated with antenna m. Let α_(i) denote the path loss of CPE C_(i). Each CPE C_(i) is a candidate for sharing a communication channel with another CPE C_(j).

Two predetermined thresholds γ₁ and Δγ, where 0≦γ₁≦1 and 0≦Δγ≦γ₁, are chosen. The Δγ is the marginal threshold of γ₁. A good guideline for the selection of Δγ is 0.1γ₁≦Δγ≦0.2γ₁.

In Step 210, for each C_(i), where 1≦i≦K, if α_(i)≧γ₁+Δγ, then CPE C_(i) is included in the set χ_(pre), i.e., χ_(pre)=χ_(pre)∪{C_(i)}. Let L denote the number of CPEs with a path loss that satisfies the above condition.

In step 220, CPE C_(i) with the smallest α_(i) is selected to be one of the two CPEs to share a communication channel. If more than one CPE has the same smallest path loss, a predetermined tie-breaker rule is employed to select only one. For example, the first of the CPEs that have the smallest path loss is selected.

In step 230, for each C_(j) in the χ_(pre), where 1≦j≦L and i≠j, the correlation s_(i) ^(j) between CPE C_(i) and CPE C_(j) is calculated according to the following equation:

$s_{i}^{j} = {{{h_{i}^{H}h_{j}}} = {{{\sum\limits_{m = 1}^{M}{h_{i,m}^{*}h_{j,m}}}}.\mspace{14mu} (\ldots)^{H}}}$

denotes a Hermitian operator. CPE C_(j) that has the smallest correlation with CPE C_(i) is identified to be a potential partner.

In step 240, for CPEs C_(i) and C_(j), a value based on spatial signatures and path loss is calculated according to the following equation: α_(i)(1−|h_(i) ^(H)h_(j)|²).

In step 250, if α_(i)(1−|h_(i) ^(H)h_(j)|²))≧γ₁, then CPE C_(j) is the other CPE that is to share a communication channel. A pair of CPEs (C_(i), C_(j)) is identified to share a communication channel and then CPEs C_(i) and C_(j) are removed from the set χ_(pre).

If α_(i)(1−|h_(i) ^(H)h_(j)|²)<γ₁, CPE C₁ cannot be the one to share a communication channel with CPE C_(j). CPE C_(i) is then removed from the set χ_(pre). If more than one CPE remains in the set χ_(pre), the selection process is repeated from step 220.

The process continues until no two CPEs could share a communication channel. All pairs of CPEs that could share a communication channel in SDMA are identified.

The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims.

Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims. 

1. A method for selecting multiple customer premises equipments (CPEs) to share a channel in a wireless communications network, the method comprising: calculating a correlation between spatial signatures of every two CPEs subscribing to a base transceiver station (BTS) of the wireless communications network, wherein two CPEs constitute channel-sharing candidates if their correlation is lower than a predetermined threshold; creating a first set of CPEs of all the member of channel-sharing candidates; counting a number of channel-sharing candidates a CPE relates to for every CPE; selecting a first CPE related to the fewest number of channel-sharing candidates; creating a second set of CPEs by identifying all the CPEs that the first CPE relates to; and selecting a second CPE related to the fewest number of channel-sharing candidates from the second set of CPEs, wherein the first and second CPEs become two selected CPEs to share the channel.
 2. The method of claim 1, wherein the channel is a multiple access channel selected from the group consisting of frequency division multiple access, time division multiple access, code division multiple access and any combination of the above.
 3. The method of claim 1, wherein the first predetermined threshold has a value between 0 and
 1. 4. The method of claim 1, wherein a predetermined tie-breaker rule is employed to select just one first CPE if more than one CPE has the same smallest number of CPEs that it could share a communication channel with.
 5. The method of claim 4, wherein the predetermined tie-breaker rule is to select the first CPE of the one or more first CPEs.
 6. The method of claim 1, wherein a predetermined tie-breaker rule is employed to select just one second CPE if more than one CPE has the same fewest number of CPEs that it could share a communication channel with.
 7. The method of claim 6, wherein the predetermined tie-breaker rule is to select the first CPE of the one or more second CPEs.
 8. A method for selecting multiple customer premises equipments (CPEs) to share a channel in a wireless communications network, the method comprising: creating a first set of channel-sharing candidates of CPEs having a path loss that exceeds the sum of a first and a second predetermined threshold; selecting a first CPE from the first set of channel-sharing candidates of CPEs by identifying the CPE having the smallest path loss; calculating a correlation between the spatial signatures of the first CPE and the first set of channel-sharing candidates of CPEs; selecting a second CPE from the first set of channel-sharing candidates of CPEs by identifying the second CPE whose spatial signature and that of the first CPE are least correlated; and calculating a value based on the spatial signatures and path loss of the first and the second CPEs and verifying if the value exceeds the first predetermined threshold.
 9. The method of claim 8, wherein the channel is a multiple access channel selected from the group consisting of frequency division multiple access, time division multiple access, code division multiple access and any combination of the above.
 10. The method of claim 8, wherein the first predetermined threshold has a value between 0 and
 1. 11. The method of claim 8, wherein the second predetermined threshold is the margin of the first predetermined threshold.
 12. The method of claim 11, wherein the second predetermined threshold has a vlaue between one-tenth and two-tenths of the first predetermined threshold.
 13. The method of claim 8, wherein if more than one CPE has the same smallest path loss, a predetermined tie-breaker rule is employed to select only one.
 14. The method of claim 13, wherein the predetermined tie-breaker rule is to select the first CPE that has the smallest path loss.
 15. The method of claim 8, wherein the value bases on the spatial signatures and path loss of the first and the second CPEs is calculated according to the following equation: α_(i)(1−|h_(i) ^(H)h_(j)|²), where h_(j) is the spatial signature of CPE i, h_(j) is the spatial signature of CPE i and α_(i) is the path loss of CPE i. 